1. Field of the Invention
This invention relates to a camera with a built-in CPU (central processing unit) for various control operations, and more particularly to a camera having a reset function for the CPU.
2. Description of the Related Art
In recent years, there have been cameras with built-in CPUs for controlling photographing operation in accordance with prewritten programs. In this type of camera, a photographing operation possible state and a photographing operation impossible state can be changed over by a switch such as a power switch provided in a camera body or a switch actuated in response to the opening and closing of a barrier of a photographing lens. When the switch is changed over to the photographing operation impossible state, it is impossible to photograph, and film is not wasted even if a release button is erroneously pushed. Moreover, in the photographing operation impossible state, the energy of a power source cell is not consumed.
Conventionally, the photographing operation impossible state has been established by the following methods:
[1] Electric power is completely shut off by turning off the above-mentioned switch; or
[2] Turning off the above-mentioned switch does not shut off power, but stops clock pulses to be applied to the CPU so that the CPU is in a standby state and a low consumed power mode is established.
The method [1] has an advantage that even if the CPU runs away and the camera operates erroneously, it is possible to recover the normal state by shutting off power and resetting the CPU (recovering the initial state of the CPU) when power is supplied again. However, since power is completely shut off from the CPU,, camera operations such as film rewinding or automatic film advancing to the first effective frame cannot be effectuated at all.
In the above method [2], even if the CPU is in the standby state, if a signal from a film rewinding switch or a switch responsive to the opening and closing of a back cover of the camera body is inputted to an interrupt terminal of the CPU, then the CPU is changed over from the standby state to the normal operating state so that film rewinding and film advancing to the first effective frame can be made. However, if the CPU runs away, the power-on reset of the above method [1] cannot be used, and the only way to recover the normal state of the camera would be drawing out the cell from the camera body. Since camera bodies tend to be made of plastic recently, static electricity will enter a terminal of the CPU so that it is more likely than ever that the CPU runs away. Therefore there has been proposed a camera using the above method [2] and provided with a separate reset switch for the CPU. However, while the user will immediately notice such runaway of the CPU as causes a film winding and rewinding motor to run endlessly and he can turn on the reset switch, the user cannot notice any runaway of the CPU which is unnoticeable from the outside, as in the case that the program enters an endless loop, and he will not turn on the reset switch. Therefore, in the latter case, the abnormal state remains, and the energy of the power source cell is wasted. Thus, when the camera is used next time, it will not operate because of an insufficient voltage of the power source cell.